Metal die-casting is a process in which molten metal, such as aluminum or magnesium is injected into a metal mold to produce a molded article. The molten metal is usually introduced into a shot sleeve which uses a piston or plunger to force the molten metal at pressure into the mold.
The properties of the molded article depend to a large extent on the quality of the molten metal introduced into the mold. Molten metal quality is adversely affected by contaminants such as dissolved hydrogen and oxide impurities. Impurities may be introduced in the molten metal in the smelting process and by exposure to atmosphere.
According to the traditional process, which is still used by many die-casting facilities, metal is initially refined by a metal smelter and cast into ingots. A die caster purchases ingots from the smelter and melts the ingots in a furnace, usually adding scrap metal from the die-casting process. As some refining is carried out in the remelting, ingot metal quality is often not as high as it should be for high quality die cast articles. Some loss of metal occurs through oxide formation on the ingot surface and hydrogen dissolution may occur in the melting process.
A significant amount of energy is wasted in re-melting an ingot as metal which has already been melted to form the ingot has to be re-melted. Typically using a conventional reverbatory furnace, this requires an energy input on the order of 2,500 BTU per pound in the case of aluminum.
Another problem associated with having a die-casting facility melt and at least partially refine its own metal arises when an increase in capacity is required. To add more die-casting equipment it is necessary to increase the ability to melt metal. This requires both capital and space to increase furnace size or the number of furnaces.
One method that has been previously used to enhance furnace capacity is to obtain molten metal from a metal smelter and pour the molten metal directly into the furnace. Molten aluminum is transportable for considerable distances (up to approximately 200 miles) using road-going vessels. Road-going vessels are in essence covered, insulated containers which may be carried on a suitably modified flat-bed trailer.
Having molten metal delivered assists in reducing the amount of furnace capacity and energy required. As molten metal is poured into the furnace, impurities are introduced through contact with the atmosphere therefore requiring at least some further refining before use. Although molten metal delivery maximizes furnace capacity, increasing production would still eventually require increasing the size or number of furnaces.